1. Field of the Invention
The present invention relates to digital image processing methods and more particularly to a method and apparatus for handling encoded image data to rotate the image.
2. Description of the Prior Art
There is a considerable amount of prior art relating to methods for processing encoded image data to achieve rotation of the original image with respect to its orientation upon input to the encoding system. Varied examples are found in U.S. Pat. Nos. 3,968,475; 3,976,872; 4,052,699; 4,168,488; 4,225,929; and 4,271,476; as well as in EPO published patent application No. 081,096 and IBM Technical Disclosure Bulletins, Vol. 13, No. 11, April 1971, page 3267; and Vol. 18, No. 8, January 1976 at pages 2633 and 2640.
In applications where the output image is displayed in raster form the image data to be processed may not be immediately available in storage for readout in raster form, that is, each binary bit may not represent a picture element or pel of the original image. The data may, for example, be stored in a run end or run length form, that is, the binary coding is representative of the transition points between black and white on the original image. In run length coding the binary numbers are indicative of the width of each black and white segment in the line of an image, while the binary numbers in run end coding cumulatively indicate successive points of transition along the line. Such representations may be compacted by a procedure such as the CCITT compression standard. One such compaction scheme is described in copending U.S. patent application Ser. No. 571,239 now abandoned. This method includes both an encoder and a decoder. The decoder may be used to create run end representations of individual lines of an encoded image.
One method of rotating an image encoded in run representation form would be firstly to convert the coded data to raster image form using the method described in U.S. Pat. No. 4,596,039 and then using either the procedure described in copending U.S. patent application Ser. No. 567,214 or the procedure described in copending U.S. patent application Ser. No. 567,293 to rotate the image data in place. All of the preceding applications are assigned to the same assignee as the present application. While these methods are valuable in themselves, their combination would usually result in a great deal of movement of data, much of which would be unnecessary. A further problem is presented by the fact that the resulting procedure would probably be unsuitable for use on systems which allocate storage in blocks that are not large enough to contain an entire image. In such systems, the image must be split among several blocks and the rearrangements necessary for the 90.degree. in situ rotation become very complicated. Consequently, for typical images, it would be more efficient to combine the steps of converting the image to raster form and rearranging the subunits (e.g., 8.times.8 pel blocks) of the image.
The present invention is directed to providing a system for combining the conversion and rearrangement of the run end or run length data and for subsequently reordering the data and rotating the subunits to create the final output images in raster form rotated by 90.degree., either clockwise or counterclockwise, or by 180.degree. from the original image orientation.
The prior art cited above neither teaches nor suggests the present invention as disclosed and claimed herein.